Many of the conference presentations focused on what is beyond silicon for solar PV module manufacturers, and efforts to push efficiency beyond the theoretical limit of this material (alone). It was also clear, however, that there is still plenty of work to be done in tweaking various elements of the silicon process to reach even higher efficiencies.
In this vein, research institute imec, based down the road from the conference in Leuven, Belgium, has done just that – hitting 23.03% efficiency with an n-type PERT (Passivated Emitter and Rear Totally diffused) cell. The efficiency has been certified by Fraunhofer ISE, and imec notes that it was achieved using a process compatible with large-scale production.
Though the industry remains more focused on p-type silicon, n-type does offer advantages, according to imec, in that it is not affected by light induced degradation – an issue, which has affected the output of many installed solar panels, and still may not be entirely solved. Philip Pieters, Business Director at imec told pv magazine that many manufacturers could use existing equipment to produce this n-type cell, eliminating the need for costly investment in new production equipment.
“Until now, nPERT solar technology has not yet found the traction it deserves in the industry,” added Loic Tous, senior researcher at imec. “With these ever-improving results, which we achieved by applying knowledge gained from our bifacial nPERT project, we are now demonstrating the potential of nPERT technology. The advantages in stability and efficiency potential over p-type PERC cells, while using the same equipment with the addition of a Boron diffusion, make this a very promising technology for future manufacturing lines.”
Tandem cells & perovskites
Tandem cells, where two or more materials tuned to absorb different portions of the light spectrum, also emerged as a key theme at EU PVSEC 2018. Although major commercial production is certainly described by University of New South Wales, Australia, Professor Martin Green in his presentation, as “the most practical route to higher efficiencies.” Green’s speech foresaw tandem cells based on silicon combinations gaining commercial acceptance over the next 10 years, and thin film tandems with up to four active layers being developed further into the future.
Imec also published a new development in this area, setting a new record efficiency at 24.6% for a perovskite/CIGS tandem cell. The cell utilizes a four terminal set up, meaning that it is essentially two separate devices operating one on top of the other. Pieters explained that while this may require a more complex system set up, with additional power point tracking required, allowing the cells to operate independently has several advantages and can increase the overall output.
The research collaboration, Solliance, of which imec is a part, also published new results at the EU PVSEC conference, demonstrating a perovsite solar cell measuring 0.09 cm², which retained 93% of its performance after 3,000 hours of testing at 85°C – showing progress in one of the main areas that has held perovskite solar cells back from commercialization. The team at Solliance said it will now focus on scaling this up to develop an industrially viable process.